So I have been working and working on my P0455 diagnostic trouble code. I have looked at all the vacuum lines, done a smoke test and am unable to find any leaks. I have been told that my Leak Detection Pump is most likely the cause of my problems. My local Jeep stealership wants over 400 bucks for this thing, and it may not even be the problem. I got a leak detection pump from my local Pull-a-part for less then 5 bucks, shut off the check engine light, and only 3 days later it is back on with the same code. I am told that these pumps go bad quite frequently. How can I tell if mine is working properly? The one that was on my XJ was making a squeeking noise when I first started the vehical in the morning, but it when away after the jeep got warm. The other one is dead silent, does this mean that it is dead? Both of them, I can not blow or suck air from where the vacuum line hooks up, but where the large tubes go, air passes freely. When I smoke test at the port next to the purge valve, I get smoke from the small air filter connected to the LDP. Is this normal? I can block off the end of that hose and smoke test and get no leaks anywhere else. My stealership won't offer any information unless they are the ones fixing it. Thanks for any help! -Jason